A reduction gear unit of the generic type is known from the prior art as a result of the use in a motor vehicle seat for driving a height setting apparatus. A first gearwheel of a second gear stage has two guide pins which engage into two guide grooves of a torque support disk. The width of the guide pins corresponds approximately to the width of the guide grooves. A relative rotation between the torque support disk and the first gearwheel is avoided as a result. However, the guide pins are arranged in the guide grooves such that they can be displaced linearly. The guide pins are in each case cuboid and are formed in one piece from a main body of the first gearwheel, in particular are pushed through out of the material of the first gearwheel. For manufacturing reasons, a transition region between in each case one guide pin and the main body has to be rounded circumferentially with a radius. As a consequence of the radius, the guide pins can jam with boundary edges of the guide grooves.
A reduction gear unit having an additional third gear stage is known from DE 10 2004 043 310 B4.